Polyurethanes are prepared from compounds with at least two hydroxyl groups and compounds with at least two isocyanate groups. See, e.g., D. Randall and S. Lee, “The Polyurethanes Book”, New York: John Wiley & Sons, 2003; and K Uhlig, “Discovering Polyurethanes”, New York: Hanser Gardner, 1999. The isocyanate groups of the isocyanate compound react with the hydroxyl groups of the hydroxyl compound to form urethane linkages. In many cases, the hydroxyl compound is a low molecular weight polyether or polyester. The isocyanate compound can be aliphatic or aromatic, and in the preparation of linear polyurethanes is typically difunctional (i.e., it is a diisocyanate). However isocyanate compounds with greater functionality are used in preparing thermoset polyurethanes. The family of polyurethane resins is very complex because of the enormous variation in the compositional features of the hydroxyl compounds and isocyanate compounds. This variety results in a large numbers of polymer structures and performance profiles. Indeed, polyurethanes can be rigid solids, soft and elastomeric, or a have a foam (cellular) structure.
Rigid polyurethane and polyisocyanurate foams are particularly effective thermal insulators. Most applications are as insulating materials in construction. However, the inherent ability of polyurethane and polyisocyanurate foams to burn creates a need for reduced flammability. See, e.g., S. V. Levchik, E. D. Weil, “Thermal decomposition, combustion and fire-retardancy of polyurethanes—a review of the recent literature”, Polymer International, volume 53, pages 1585-1610 (2004). Polyurethane and polyisocyanurate foams also exhibit high moisture absorption, with the absorbed moisture acting as a plasticizer that detracts from the physical properties of the foams.
There is therefore a need for polyurethane and polyisocyanurate foams exhibiting improved resistance to burning and/or reduced moisture absorption.